Conventional golf balls can be divided into two general classes: solid and wound. Solid golf balls include one-piece, two-piece (i.e., solid core and a cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material, and a cover. It is also possible to surround a hollow or fluid-filled center with a plurality of solid layers. Solid balls have traditionally been considered longer and more durable than wound balls, but many traditional solid constructions lack the “feel” provided by the wound construction.
By altering ball construction and composition of solid balls, manufacturers recently have been able to vary a wide range of playing characteristics, such as compression, velocity, “feel,” and spin, optimizing each or all be optimized for various playing abilities. In particular, a variety of core and cover layer(s) constructions, such as multi-layer balls having dual cover layers and/or dual core layers, have been investigated and now allow many non-wound balls to exhibit characteristics previously not maintainable in a solid-construction golf ball. These golf ball layers are typically constructed with a number of polymeric compositions and blends, including polybutadiene rubber, polyurethanes, polyamides, and ethylene-based ionomers.
Highly neutralized polymers of ionomers, and in particular ethylene-based α,β-ethylenically unsaturated carboxylic acid copolymers or a melt processible ionomer thereof, are a preferred polymer for many golf ball layers. However, one problem encountered with the use of ionomers as stiff layers is the unprocessability of the material as the percent of neutralization of the acid group increases. Ionomers are stiffened by increasing the amount of neutralization by a metal cation or a salt thereof. Once the percent of neutralization is greater than about 60% (depending on metal cation selected), the melt flow of the ionomer becomes too low and the ease of processability decreases or disappears altogether.
Diene rubber or some form thereof, which provides the primary source of resiliency for the golf ball, has been used as the material for most conventional solid cores. The core of solid golf balls is the “engine” of the ball, providing the velocity required for good distance. Too hard a core, however, can result in a golf ball that provides poor feel. Compositions of this type are constantly being altered in an effort to provide a higher coefficient of restitution (COR) while at the same time resulting in a lower compression which, in turn, can lower the golf ball spin rate, provide better “feel,” or both.
A dynamically vulcanized alloy is a representation of a blend of two polymeric components such that one polymeric component is vulcanized or crosslinked dynamically in the presence of another polymeric component that is not covalently crosslinked. Dynamically vulcanization is a method of making new polymeric materials from existing polymeric components. DVA also implies that an intimate mixture of both blend components is formed as a result of crosslinking while the components are mixed. In this invention, an HNP and a DR may be blended such that the DR is dynamically vulcanized to form an alloy in the presence of the HNP that remains essentially not covalently crosslinked. DVA of two polymeric components will exhibit properties that are in between those of the pure polymers.
On the other hand, an interpenetrating polymer network is a representation of heterogeneous materials in which the polymeric components are cross-linked within the kinds. As a result, the IPN will not result in some cases in a phase-separated situation. Therefore, an IPN of different polymers will also exhibit properties that are at least in between those of the pure polymers, and sometimes the new material shows a synergistic increase of the properties of the polymers. In a thermoplastic IPN, components are mixed together but not chemically crosslinked.
Perimeter weighted (PW) golf balls provide better control of spin rate, which is an important feature for both skilled and recreational golfers. High spin rate allows the more skilled players to produce and control back spin to stop the ball on the green and side spin to draw or fade the ball. In contrast, recreational players prefer a low spin golf ball which tends not to drift off-line erratically if the shot is not hit squarely off the club face. The control of the spin rate of golf balls can be achieved by reallocating the density or specific gravity of the various layers or mantles in the ball. When the weight from the outer portions of the golf ball is redistributed to the center, the moment of inertia decreases and the spin rate increases. When the weight from the inner portion of the golf ball is redistributed outward, as in the case of a PW golf ball, the moment of inertia increases and the spin rate decreases.
However, the art does not provide golf ball compositions comprising a blend of HNP and DR that are in IPN to make highly resilient, durable and tailorable golf ball components that show a wide range of hardness and modulus properties as well as PW characteristics.